1. Field of the Invention
The present invention relates to electronic private branch exchanges which have a function to cause a plurality of specific extension telephone sets to respond to an incoming signal from a corresponding main wire trunk and, more particularly, to electronic private branch exchanges which are capable of changing extension telephone sets which are caused to produce an incoming signal tone as needed according to time zones.
2. Description of the Related Art
Conventionally there have been used two types of reception of an incoming signal to a private branch exchange from a main wire trunk, one being first by an attendant console and the other being directly by an extension telephone. The latter is a so-called "direct inward dialling system". In the direct inward dialling system, generally there are provided a plurality of extension telephone sets for reception of an incoming signal from the corresponding one of the main wires. For example, a plurality of extension telephone sets can simultaneously receive and each respond to an incoming signal from the corresponding main wire trunk. Generally, high function telephone sets (EKTs) each have a particular one of a plurality of button keys allocated to the corresponding main wire. When there is an incoming signal from that main wire, a light emitting diode (LED) for the particular key of each EKT flashes, and the incoming tone is produced simultaneously at that particular EKT. In order to respond to the incoming signal, the flashing key of the EKT may be only pressed.
Another such direct inward dialling system using EKTs is to only flash a LED for the particular key of each EKT without producing an incoming signal tone.
A further direct inward dialling system is the simultaneous use of a subsystem in which an incoming signal is reported both by production of an incoming signal tone and by flashing of a LED for an EKT and a second subsystem in which an incoming signal is reported only by flashing a LED for another EXT.
The effect of this system is that particular ones of the EKTs which respond to an incoming signal are virtually determined. In other words, an incoming signal tone is be required to be produced only at particular EKTs for persons responsible at all times for responding to the incoming signals at all times. Usually, production of an incoming signal tone at particular telephone sets is effective for only persons who must respond to that incoming signal and other incoming signal tones are only noisy to those persons.
Whether particular EKTs are set to produce an incoming signal tone when there is an incoming signal is determined on their installation, so that change is not easy. Thus such EKTs are inconvenient when they are desired to be switched between production and non-production of an incoming signal tone according to time zones. In the use of a direct inward dialling system at general business firms, different persons may be concerned as responders with the direct inward dialling system generally according to time zones such as morning, lunch time, afternoon or night. Also, in such a case, incoming signal tones were produced at particular EKTs in the past.
Setting of production or non production of an incoming signal tone at particular EKTs in the direct inward dialling system is virtually half-fixed conventionally and it is not easy to change such EKTs to others also according to time zones.
It is therefore an object of the present invention to eliminate such problems to thereby allow switching between production and non-production of an incoming signal tone at particular EKTs according to time zones.